Hydrogen production by catalytic decomposition of methane over Fe based bi-metallic catalysts supported on CeO2–ZrO2

Abstract

Methane decomposition to produce hydrogen was studied over iron based bimetallic catalysts supported on cerium-zirconium oxide in a continuous flow fixed bed reactor at 700 °C. 15 wt% Fe/CeZrO2 was prepared by wetness impregnation and the promoted Fe catalysts (15 Fe-5 Co/CeZrO2 and 15 Fe-5 Mo/CeZrO2) were prepared by co-impregnation technique. Mo promoted Fe catalyst exhibited the maximum surface area of 24.08 m2/g. X-ray diffraction studies revealed that Fe2O3, Co3O4 and MoO3 were the phases present in freshly calcined catalysts, while the reduced catalysts consisted of phases including elemental Fe, Mo and Fe–Co alloys. Both X-ray diffraction and temperature programmed reduction studies confirmed the complete reduction of metal oxide species under H2 at 700 °C. The catalytic activity of Fe/CeZrO2 was enhanced upon addition of Co and Mo as promoters. The initial hydrogen yield on 15 Fe-5 Mo/CeZrO2 was ~90% and it decreased with increase in time on stream (TOS), and finally stabilized around ~50% after 125 min of TOS. The Co promoted catalyst exhibited similar activity while the initial hydrogen yield on 15 Fe/CeZrO2 was ~83% and dropped to ~33% after 125 min of TOS. Graphitic carbon, Fe3C and Mo2C phases were observed in the XRD patterns of spent catalysts along with elemental Fe and Fe–Co alloy. It was evident from temperature programmed oxidation results that coke formation which deactivates the catalyst was dominant in 15 Fe/CeZrO2 when compared to the promoted (Co and Mo) Fe catalysts where carbon nanostructures were dominant. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the formation of carbon nanostructures on the surface of spent catalysts. The Fe based catalysts supported both tip and base-growth mechanisms for the growth of carbon nanostructures.